Lipids are a diverse group of organic compounds that contain carbon, hydrogen, oxygen, nitrogen and phosphorus. They are non-polar and hydrophobic, meaning they are insoluble in water but soluble in organic solvents. Lipids include triglycerides, phospholipids, waxes, steroids, and terpenoids. They serve important structural and energy storage functions in living organisms.

1. LIPIDS
• Lipids are a diverse group of organic compounds
• Lipids contain carbon,hydrogen,oxygen,nitrogen and
phosphorous
• Lipids are non-polar and hydrophobic compounds i.e
insoluble in water
• They are easily soluble in organic solvents like ether,
alcohol, chloroform, benzene etc
• Lipids store double the amount of energy as compared
to carbohydrates and proteins because
• They contain high proportion of C-H bonds & very low
oxygen as compared to carbohydrates and proteins
• Act as insulating layer e.g. waxes in exoskeleton of
insects
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2. Classification of of lipids
• Lipids are classified into various groups;
• 1 Triglycerides
• 2 Phospholipids
• 3 Waxes
• 4 Steroids
• 5 Terpenoides
• Triglycerides (tri-three, glycerides-Glycerol)
• Also known as Acylglycerol.
• Triglycerides are generally called Fats.
• Chemically triglycerides are ester of fatty acids and
alcohal
• They are composed of :
• Glycerol…..One molecule
• Fatty acid….three molecules
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3. Triglycerides
• Glycerol:
• It is an alcohal,consist of three carbon atoms. Hydroxyl
(OH) is attached to each Carbon. Hydroxyl group are
polar in nature; hence glycerol is soluble in warter
• Fatty acids:
• Fatty acid consist of a hydrocarbon chain, to which a
single carboxyl (-COOH) group is attached at the
terminal end.
• Fatty acid contain even number of carbon atoms e.g.
2,4,6,8,10,12,14,16,18,upto 28.
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4. Fatty acids types
• Two types of fatty acids
• 1. Saturated fatty acids:
• These fatty acids have no double bonds between carbon
atoms
• Can’t accommodate any more hydrogen atoms
• Solid at room temperature
• Stored in animals as fats. Example is Palmatic acid (16-C)
• Unsaturated fatty acids:
• They have one or more double bonds between carbon
atoms.(C=C)
• Accommodate any more hydrogen atoms
• Liquid at room temperature
• Stored in plant seeds. Example is Oleic acid (18-C)
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5. 2.Phospholipids
• A class of lipids that are a major component of all cell
membranes as they can form lipid bilayers.
• Composition: phospholipids are composed of
• i. Glycerol: one molecule
• ii. Fatty acids :Two molecules
• iii. Phosphoric acid: one molecule
• When a nitrogen containing group is attached with phosphate
end of phospholipids, it is known as Phosphatidyl Choline.
• Phospholipids have two parts
• i) Head:
• Head is polar in nature, Soluble in water (Hydrophilic).
• ii) Tails:
• Tail is non-polar in nature, insoluble in water (Hydrophobic)
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6. Phospholipids

7. 3.WAXES
• Waxes are derived lipids.
• Waxes is ester of saturated fatty acid and long chain
alcohol
• Composition: waxes are composed of
• i) long chain fatty acid.... One molecule
• ii) long chain alcohol having a single hydroxyl group(-OH) e.g.
Cetyl alcohol
• waxes are hydrophobic in nature.
• Have high melting point, hence solid at room temperature.
• show stability & are resistant to degradation.
• On the surfaces of plant parts e.g. leaves & fruit,they form
a water proof layer, hence reduce rate of transpiration.
• Waxes also form waxy layer, which cover animal bodies
e.g.Sheep,insects etc.
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8. 4.Steroids
• Steroids comes under the category of lipids
• Steroids are derived lipids
• Composition: Contain a characteristic arrangement of
• 3 Cyclohaxane ring
• 1 Cyclopentane ring, a total of 17-carbon atoms in four
fused Carbon ring.
• Steroids do not contain alcohol and fatty acids
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9. Steroids
• Examples of steroids:
• i) Cholesterol:
• An important component of animal cell membrane.
• Precursor molecule of all hormones such as
aldosterone, sex hormone and Vitamin D
• ii) Aldosterone helps to regulate Na+ ions in the blood
• iii) Sex hormones e.g. testosterones, progesterone,
estrogens help to maintain male and female
characteristics
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10. Terpenoides
• Are large and diverse class of naturally occurring organic
compounds
• Terpenoides are lipid derivatives, lipid soluble & water
insoluble
• Do not contain fatty acids like steroids.
• Composed of units known as isoprenoid units or isoprene
units
• Isoprene unit: five carbon hydrocarbon with a branched
chain structures.
• Isoprene units join together by condensation process
resulting different type of compounds e.g. Carotenoides,
terpenes and rubber etc
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11. Carotenoides
• Carotenoides are yellow,orange,red or brown pigments in
plants
• They are of two types
• i) Carotene: ii) xanthophylls
• i) Carotene:
• Orange, red in Colour, beta carotene is a type of
carotene. Present in carrot & rice.
• The breakdown of beta carotene in human body yields two
molecules of Vitamin A.
• ii) Xanthophyll: Accessory pigments
• yellow in colour found in leaves of plants.
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12. Functions of lipids
• 1.Structural building material:
• Lipids act as structural building material e.g. cell
membrane is composed of lipo-protein molecules.
• 2.Source of energy:
• Contain twice the amount of energy due to greater
number of C-H bonds as compared to Carbohydrates
and proteins.
• 3.As insulator:
• Lipids provide insulation to various organs of animals
and also act as lubricants
• 4.Regulate of vital chemical reactions:
• hormones which are steroids, regulate many vital
process in both plants and animals
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